Funds are requested to purchase a high performance LC/MS/MS system equipped with electrospray, nanospray and atmospheric pressure chemical ionization sources for the UCLA Pasarow Mass Spectrometry Laboratory. This is a shared facility jointly supported by the Department of Chemistry & Biochemistry (College of Letters and Sciences) and the Department of Psychiatry & Biobehavioral Sciences and the Neuropsychiatric Institute (School of Medicine) that is available to the entire UCLA campus research and teaching enterprise. The driving force behind this application is the need for an instrument that can be devoted to analyses of brain dialysate tissue perfusion biopsy samples for the specific quantification of multiple neurotransmitters and related compounds in the same samples, and for the identification of novel neuro-regulatory compounds, which are co-released with known neurotransmitters. At least seven different laboratories on the UCLA campus will use this instrument in their research. The extreme demands for sensitivity in this research require an instrument that can be reserved for operation at absolute maximal efficiency. There is no instrument on the UCLA campus, which is available and suitable for this type of research and these types of samples. This instrument will be a central analytical tool of the growing cadre of UCLA scientists who use brain dialysis as a core experimental technique, and the acquisition of this instrument is essential for the continued productivity, success and competitiveness of these programs. The PI and his associates have carefully evaluated all available instruments which potentially fulfill the demanding requirements, and have chosen the Q Trap Pro LC/MS/MS system package from Applied Biosystems as the most suitable of those currently available. Descriptions of the research of the seven major users of the instrument are provided.